Moving alog to bigger projects with more power consumption I began to read more on properly powering the Arduino, however I still wonder about what the right way in certain situations is.
My scenario:
Arduino Mega + Multiple modules, LCD, sensors + serial communication with PC over USB port
I need to power many peripheral devices that require a 5V supply or reference voltage and I don't want to overload the onboard 5V voltage supply. I could use an external 5V regulator and connect all my devices and the Arduino 5V pin to this supply to bypass current away from the Arduino's onboard voltage regulator.
However, I read that powering Arduino through the 5V pin is a "dangerous game" with zero tolerance for mistakes. Some suggest using the USB port to supply the 5V, but I am already using it for serial communication.
Moreover, I read that Arduino automatically switches from USB to "Jack" power supply if detected, which is not the case on the 5V pin. What would happen if I had a USB and a 5V power supply connected at the same time?
To sum up: Any suggestions on how to simultaneously do the following 3 things:
USB serial communication
Power the Arduino
Have an external 5V reference/supply voltage that bypasses the onboard regulator and is identical to the 5V pin on Arduino
What would happen if I had a USB and a 5V power supply connected at the same time?
While it is not recommended nothing much would happen. Depending on what supply was the biggest you would get a bit of current going from one supply to the other. I do it most of the time without incident yet.
With 7.5volt on the DC socket, you can draw quite a bit from the Mega's 5volt supply before the regulator gets too hot.
Why don't you list the "Multiple modules, LCD, sensors", so we can check.
Leo..
In a perfect scenario, one 5V power supply could provide for many devices ... The supply would have no voltage sag under load, with perfect voltage stability and the output impedance Z would be 0 Ohms.
But, in reality, high current devices need to be on a separate power leg ... So motors should be separated from digital logic. This can be done with separate regulators or one large power unit with proper filtering:. Low resistance wires and tantalum caps as close as possible to current consumption devices.
I have been using the low cost DC-DC converters to provide separate power nodes and filtering. At around $1 or less each per "node" and with common grounds, these work great for Arduino 5V or 3.3V or even mixed voltage projects. At 93% or better efficiency, these are superior solutions to power issues in digital logic.
Sounds like a perfectly simple job for CrossRoads.
Make a blank shield and passthrough all the pins but the 5v, which would be routed to an external jack, and the deluxe board could have screw terminals too. A few leds n resistors and presto, you have a way to stack a bunch of high power shields with external power on the normal 5v pins and all grounds would already be connected via pins.
Moreover, I read that Arduino automatically switches from USB to "Jack" power supply if detected, which is not the case on the 5V pin.
The 5V pin is the output of the 5V regulator, or the 5V from USB thru a MOSFET that has been discussed in the past as looking like it's wired backwards. The USB is not used to drive 5V if Vin/2 is > 3.3V, otherwise USB power is used.
If you take my Mega screw shield and cut a couple of 5V traces to isolate the 5V header from the rest of the board, you could add a higher current switching regulator and power all the external components you wanted while leaving the USB to power the Mega.
Wawa:
Why don't you list the "Multiple modules, LCD, sensors", so we can check.
Roughly listed would be the following:
Ethernet Shield
Seedstudio CAN bus shield
LCD screen (16x2)
Adafruit ADC 16bit, 4 channel module
Adafruit DAC 12 bit module
Load cell
5k potentiometer position sensor
cca. 10 buttons & limit switches
CrossRoads:
If you take my Mega screw shield and cut a couple of 5V traces to isolate the 5V header from the rest of the board, you could add a higher current switching regulator and power all the external components you wanted while leaving the USB to power the Mega.
Hard/impossible to find all the curent draws of these devices, but an educated guess is about 400mA total.
Just possible to power that from USB, and 7.5volt on the DC socket would be a safe way for external power.
The regulator would dissipate ~0.75watt. Just ok long term for a Mega.
9volt on the DC socket could be too much (regulator getting too hot).
Leo..